A mass spectrometry (MS) system in general includes an ion source for ionizing molecules of a sample of interest, followed by one or more ion processing devices providing various functions, followed by a mass analyzer for separating ions based on their differing mass-to-charge ratios (or m/z ratios, or more simply “masses”), followed by an ion detector at which the mass-sorted ions arrive. An MS analysis produces a mass spectrum, which is a series of peaks indicative of the relative abundances of detected ions as a function of their m/z ratios.
Gas filled ion guides are an example of ion processing devices positioned in the process flow between the ion source and the mass analyzer. A gas filled ion guide may be positioned near the ion source, where the ion guide may transport ions through one or more pressure-reducing stages that successively lower the gas pressure down to the very low operating pressure (high vacuum) of the analyzer portion of the system. A gas filled ion guide may also be positioned in a collision cell, where the ion guide may function as the collision cell or may be used to reduce the beam dimensions for a later stage of the system. In both cases, the ion guide serves multiple functions: a) transport the ions through a region containing a gas with few ion losses, b) transport the ions through a vacuum stage (pressure reducing) wall, c) reduce the emittance of the ion beam (obtain a smaller product of beam cross section and divergence), and d) accomplish all of the foregoing functions over close to the full mass range of the instrument.
A number of existing designs are available that accomplish many of these goals reasonably well. However, an ongoing need exists for further improvements in the design and performance of ion guides. For example, it would be desirable to make improvements in ion transmission over wider mass ranges and/or with larger pressure reductions than is possible with current designs. It would also be desirable to reduce the cost of the current ion guides or the systems containing them.